The system of the present invention has application especially in connection with the operation of heavy cyclical centrifugal machines of the type used in the manufacture and refining of sugar.
The known systems for controlling the loading of charge material into the baskets of such machines do not adequately enable compensation for variations in the loading properties of the charge material to be processed. Such variations often occur from one batch to another, and even between earlier and later operations with different portions of the same batch, of a charge material such as sugar massecuite. When they occur they may adversely affect the uniformity of basket loading needed from cycle to cycle for efficient centrifugal processing. For example, a high fluidity can lead to overfilling of or even spillage of charge material from the basket; while with a viscous, slowly flowing charge material a sudden gate closing can leave the basket unevenly loaded, thus causing rough, unbalanced running of the machine.
Variations of loading properties of the charge material are often difficult or even impossible to avoid. In the case of sugar massecuites, for example, their amenability to being loaded into and processed in centrifugal machines will vary with numerous factors among which are the massecuite temperature, sugar grain size, degree of crystallization, syrup purity, and hydrostatic pressure head in the material supply tank.
Various proposals have been made to improve the speed and the control of centrifugal basket loading operations. U.S. Pat. No. 2,727,630 (Hertrich) discloses a system making use of a charge measuring device that is changed in position as the volume of the basket charge increases during loading of the basket. The loading gate is progressively closed as the charge measuring device is displaced by progressively increasing charge wall thickness in the basket, until the basket charge approaches the final desired volume. Then the gate is maintained at a pinched or largely closed position slowing flow of the material, until the final desired volume is reached. The gate then is quickly closed so that only a small amount of material can flow through the gate as it moves from the pinched to the fully closed position.
U.S. Pat. No. 3,011,641 (Huser) discloses a mechanism for preventing overloading of the basket when employing a manually controlled loading gate.
U.S. Pat. No. 3,079,046 (Goodwin) discloses a mechanism for adjusting the extent of opening of the loading gate in accordance with pressure conditions sensed in the loading spout of a supply tank holding the material to be processed in centrifugal operations, thus adapting the extent of gate opening to variations of the hydrostatic pressure head in the tank.
U.S. Pat. No. 3,141,846 (Laven, Jr.) discloses a mechanism making use of a mechanical charge feeler within the centrifugal basket, to be positioned by the charge wall being formed in the basket in each loading operation and thus controlling the thickness of the basket charge.
U.S. Pat. No. 4,229,298 (Bange) discloses a method and apparatus for controlling the thickness of the charge wall being formed in the basket in each loading operation, wherein an electrical capacitance is established across the charge space inside the basket and a signal for regulating the loading is obtained by sensing the change of capacitance that results as the charge wall thickness is increased by the inflow of charge material.